They're probably including it for folks that have the 1st VF-31F.
This is Google Translate for this part.:
NEW Two types of connection parts are equipped as standard.
Two types of connection parts (for fighter/gerwalk, for battroid) that reproduce the success in the theater version are included. It can also be mounted on "DX Chogokin VF-31F Siegfried (Messer Elefeld machine)" now on sale. As the theater version specification, it adopts coloring which reproduced the battle of outer space.
It specifically states can be mounted for DX VF-31F VF-31F ジークフリード
Not Movie version VF-31F 劇場版VF-31F ジークフリード